1. Field of the Invention
The invention is a dual purpose bicycle chainline control using an idler cog mounted preferably in connection with a pivoting bicycle rear suspension so as to control chainline in both vertical and transverse directions thereby eliminating both chain movement induced by suspension movement and suspension movement induced by pedaling and other rider induced movement. The transverse directional control enables the idler cog to function as a high precision derailleur enabling greater flexibility in the size and range of front chainwheels on a bicycle.
2. Description of Related Art
The prior art includes three categories of devices. First are chainline and chain protection devices which are occasionally fitted to bicycles such as "mountain bikes" to prevent chains from disengaging from the chainwheels during the forceful and repetitive impact induced particularly during downhill mountain bike riding and racing. These include a variety of clips and guards, occasionally adapting rear derailleur chain tensioner pulleys or cogs to locations above and below the "normal" longitudinal chainline. These are used to provide some level of control to retain the chain against chain throw, slap and suck, these being, respectively, the chain being thrown off the chainwheel, the chain moving rapidly in a direction generally perpendicular to its axis and the lower, return run becoming overridden by the drive run.
The second major category of related art is the derailleur art. These include front derailleurs and rear derailleurs. Front derailleurs have typically simply involved a front derailleur cage having side pieces or plates that simply force a chain transversely from one chainwheel to an adjacent chainwheel on a front crank assembly typically having two or three very large chainwheels. Contact with the chain is not only not anticipated but in fact would be an indication of improper adjustment. Various art uses cage shape and pivot arrangements to minimize contact between the cage and the chain which may affect vertical chainline. The front derailleur is typically located in a position above the front chainwheel and operates to deflect the drive run or upper portion of the chain.
Rear derailleurs have been used to move a chain transversely by deflecting the return or unloaded lower run of the chain. Rear derailleurs are typically mounted in a position near and below the position of their axle of the rear wheel of a bicycle. Typically the rear derailleur moves transversely using a lever pivotally mounted on the derailleur itself, linkage or combination of these to force the chain in a transverse direction inwardly or outwardly to engage from about five to up to about eight or nine different sprockets on a rear freewheel or free hub which enables coasting while not pedaling.
As the rear derailleur is below the line between the rear axle and the bottom bracket around which the pedals crank, and is associated with the return run or lower unloaded run of the chain, coupled with the fact that the variation in size of rear sprockets and front chainwheels, in combination with varied shifting patterns, would normally require a different length of chain, the slack, the rear derailleur cage typically includes a pivoting cage having two pulleys or cogs, being spring loaded to take up chain tension. This is accomplished, however, on the unloaded return run of the chain.
Third, certain prior art has used cogs bearing on the drive run of a bicycle chain for the purpose of sensing load on the chain. Typically these load sensors are used in "automatic" shifting on bicycles. These embodiments use a cog which reacts to vertical chainline and does not control it.